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Ivo Dinov
UCLA Statistics, Neurology, LONI, Math/PIC

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STAT 13 (1a, 1b, 1c, 1d)	*Introduction to Statistical Methods for the Life and Health Science*
Department of Statistics	Instructor: Ivo Dinov
Homework 1	Due Date: Wednesday, Jan. 13, 2010

Please, submit your homework right before lecture on the due date. See the HW submission rules. On the front page include the following header.

(HW_1.1) A dendritic tree is a branched structure that emanates from the body of a nerve cell. As part of a study of brain development, 36 nerve cells were taken from the brains of newborn guinea pigs. The investigators counted the number of dendritic branch segments emanating from each nerve cell. The numbers were as follows:

DendriticSegments
33
30
54
28
31
29
34
35
28
27
21
43
51
35
51
49
35
27
26
29
21
29
37
27
28
33
33
31
37
17
20
48
41
20
30
55

(a) Construct a stem-and-leaf diagram of the data by hand.
(b) Construct a dotplot of the data, using SOCR Charts (Select Dot-Plot).

(HW_1.2) Consider the data presented in HW_1.1. Construct a frequency distribution and display it as a table and as a histogram, use SOCR Charts (Select Histogram Plot).

(HW_1.3) The histogram below (right) shows the same data that are shown in one of the four boxplots (left). Which boxplot goes with the histogram? Explain!

(HW_1.4) Dopamine is a chemical that plays a role in the transmission of signals in the brain. A pharmacologist measured the amount of dopamine in the brain of each of seven rats. The dopamine levels (nmol/g) were as follows:

7.1

5.6

5.9

6.2

7.4

6.4

coefficient of variation

(HW_1.5) Here are the 20 measurements of preening time:

PreeningTimes
27
21
10
16
62
76
33
31
46
24
8
26
57
32
25
48
22
48
29
39

SOCR Charts (Select Box-Plot)

(HW_1.6) A geneticist counted the number of bristles on a certain region of the abdomen of the fruitfly Drosophila melanogaster. The results for 119 individual fruitflies are shown in the table below.

Number_of_Bristles	Number_of_Flies
29	1
30	0
31	1
32	2
33	2
34	6
35	9
36	11
37	12
38	18
39	13
40	10
41	15
42	10
43	2
44	2
45	3
46	2

(a) Find the Median number of bristles.
(b) Find Q1 and Q3.
(c) Make a boxplot of the number of flies.
(d) The sample (number of bristles) mean is 38.45 and the sample SD is 3.20. What percentage of the observations fall within 1 SD of the mean?

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